Overview of deep water acoustics

Abstract

<p indent=0mm>The aim of research on ocean acoustics is to reveal the phenomenon and physical mechanism of sound propagation in complex marine environments, which is the basis of the high technology and application of underwater acoustics. From the view of the sound field in deep ocean and SONAR application, the progress of ocean acoustic theories and experiments by developed countries has been reviewed firstly. The history of basic research in China is introduced briefly. In 1997 and 2012, the progress of ocean acoustics in China has been summarized at the First and Third International Conference on Shallow Water Acoustics, respectively. In recent years, with the development of maritime strategy, research on ocean acoustics in China is moving from shallow water to deep water. Some progress on deep water acoustics has been made based on the funding from the Global Change and Air-sea Interaction Project and the National Natural Science Foundation of China. The scientific research achievements on deep water acoustics are reviewed from the aspects of acoustic experimental technology, sound propagation in complex ocean environments, sound field spatial correlation, characteristics of ambient noise and application on ocean tomography, ocean reverberation, geoacoustic inversion, and source localization. The distributed sound signal recorders are developed which can work at the maximal depth of <sc>12000 m.</sc> Experiment data from the South China Sea, the Pacific Ocean and the Indian Ocean surveys have been recorded with them. Three-dimensional propagation phenomena with the presence of seamount and trench-slope basin have been observed and explained by ray theory. Characteristics of spatial correlation of sound field for different ocean environments have been investigated. The sound field fluctuation and the probability distribution of the transmission losses (TLs) caused by internal waves, mesoscale eddy, surface waves and bottom roughness are systematically studied. Longitudinal and vertical correlations within the direct zone and convergence zone are relatively high for the main energy coming from the rays reflected by sound channel. Then long-time ambient noise measurements with typhoon passing by the submerged buoys have been done. The noise model for the South China Sea has been developed. A passive ocean tomography method from ambient noise is proposed to estimate sound speed profile. A geoacoustic inversion method for deep water environments is proposed by using the TLs in the shadow zone, which is very sensitive to bottom parameters. By using the relationship of arrival angle and source ranges, three source localization methods have been proposed, which can estimate the source depth and range at the same time with high precision. Finally, the key research directions of deep water acoustics are given, such as characteristics of sound field in typical ocean environments, effects of ocean environments on SONAR performance, weak signal enhancement methods based on the interference of multi-path arrivals, and environment measurements and target detection methods with unmanned platforms. It has reference meaning for future work of deep water acoustics.